Glaucoma is a condition characterized by an increase in intraocular pressure. Increased intraocular pressure can lead to optic nerve damage and defects in the visual field. Blindness can result if the condition is left untreated.
For some time two categories of drugs have been used to treat increased intraocular pressure. The first category is known as miotic agents and comprises cholinergic stimulating agents, such as pilocarpine, and cholinesterase antagonists, such as demacarium bromide and echothiopate iodide. Miotic agents are used to facilitate outflow of the aqueous humor.
Pilocarpine has been used topically to treat glaucoma for many years and has no adverse systemic effects. However, localized adverse effects are known. Ciliary spasms may lead to debilitating myopia. Irritation and allergic reactions may require discontinuation of use. Of special concern is the known ability of miotic agents to cause retinal detachment.
The cholinesterase antagonists may have systemic adverse effects including salivation, urinary incontinence, diarrhea, profuse sweating, muscle weakness, respiratory difficulties and cardiac irregularities. Localized effects include irritation, induced myopia and lens opacities.
The second category of drugs used to treat increased intraocular pressure act by inhibiting the secretion of aqueous humor by the ciliary processes. Epinephrine, beta adrenergic antagonists such as timolol and carbonic anhydrase inhibitors such as acetazolamine are members of this second category.
Topical epinephrine must be used with caution in individuals with hyperthyroidism, hypertension, cardiac disease and bronchial asthma, due to possible systemic effects. Topical beta-adrenergic antagonists must also be used with caution due to a variety of systemic effects. Timolol must be used cautiously in patients with asthma, chronic obstructive pulmonary disease or sinus bradycardia. Carbonic anhydrase inhibitors are administered systemically when intraocular pressure cannot be controlled with known topical agents. Agents such as acetazolamide often cause numbness and tingling, drowsiness and loss of appetite.
Recently it has been disclosed (U.S. Pat. No. 4587258, E. H. Gold et al., issued May 6, 1986; U.S. Pat. No. 4442089, Z. P. Horovitz, issued Apr. 10, 1984; PCT Patent Application No. W087/02585, R. W. Watkins et al., published May 7, 1987; PCT Patent Application No. W087/00055, R. W. Watkins et al., published Jan. 15, 1987; European Patent Application No. EP174162, G. Allan et al., published Mar. 12, 1986; European Patent Application No. EP114333, R. W. Watkins, published Aug. 1, 1984) that angiotensin converting enzyme (ACE) inhibitors are useful for treating glaucoma.
When renin is released into the blood from the kidney, the renin-angiotensin system is activated, leading to vasoconstriction and conservation of sodium, both of which result in increased blood pressure. The renin acts on a circulating protein, angiotensinogen, to cleave out a fragment called angiotensin I (AI). AI itself has only slight pharmacologic activity but, after additional cleavage by a second enzyme, angiotensin converting enzyme (ACE), forms the potent molecule angiotensin II (AII). The major pharmacological effects of AII are vasoconstriction and stimulation of the adrenal cortex to release aldosterone, a hormone which causes sodium retention. AII is cleaved by an aminopeptidase to form angiotensin III (AIII), which, compared to AII, is a less potent vasoconstrictor but a more potent inducer of aldosterone release.
The renin-angiotensin system has been modulated or manipulated, in the past, with ACE inhibitors to reduce blood pressure. However, ACE acts on several substrates other than angiotensin I (AI), most notably the kinins which cause such undesirable side effects as pain, "leaky" capillaries, prostaglandin release and a variety of behavioral and neurologic effects. Further, ACE inhibition leads to the accumulation of AI. Although AI has much less vasoconstrictor activity than AII, its presence may negate some of the hypotensive effects of the blockade of AII synthesis.
Most recently it has been disclosed (PCT Patent Application No. W08702581, R. W. Watkins et al., published May 7, 1987) that renin inhibitors are useful for treating glaucoma. There are no known side effects which result when renin is inhibited from acting on its substrate. While much research effort has been directed to developing renin inhibitors, there is still a need for more potent renin inhibitors.
Thus, methods and compositions for treating glaucoma or reducing and/or controlling intraocular pressure which have reduced potential for localized and systemic adverse effects, as well as increased potency, are desirable.